1. Field of the Invention
This invention relates to stringed musical instruments having fretted fingerboards, such as guitars. More particularly, the invention relates to a device for allowing harmonic tones to be played on selected strings of such instruments without the need for the player to use his or her chording hand.
Instruments of the type with which my invention is used, such as guitars, include a body from which extends an elongated neck. The top surface of the neck comprises a fingerboard to which is fastened a series of parallel transverse raised ribs, or frets, spaced along its length At the outer end of the fingerboard is mounted a transverse bar generally called the "nut"; a second transverse bar, generally called the "saddle bridge", is mounted near the end of the body opposite the neck. A number of more or less parallel tone-producing strings under tension have their ends attached respectively to the body of the instrument and to tensioning pegs near the end of the neck; between the fastening points, each string passes over the nut and the saddle bridge of the instrument. The nut and saddle bridge serve both to support the strings at a small distance above the frets and to define the so-called "open" string length--i.e. the distance, between nut and saddle bridge, over which a plucked string is free to vibrate when otherwise untouched.
The pitch produced by a string can be changed by changing either the string's tension (more tension raises the pitch) or its effective length (shorter effective length raises the pitch); the former is obviously impracticable when playing the instrument, so effective length changes are used by players to play melodies or chords.
The most common way to change a string's effective length, which I will call "standard fingering" herein, is by the player using his or her finger to press the string firmly against the fingerboard between frets, which causes the string to bear on the adjacent fret nearest the saddle bridge of the instrument. Such contact with the fret shortens the vibrating length (or effective length) of the string, resulting in a higher pitch.
A second method of changing effective string length, which I will call "harmonic fingering" herein, is based on the fact that lightly touching a string at certain defined harmonic points will cause it to vibrate at a multiple of its open frequency. In harmonic fingering, the contact must be sufficient to stop vibration at the contact point but light enough that the string is not caused to contact either a fret or the fingerboard; optimum effectiveness is achieved when pressure on the string is the minimum required to stop vibration. For example, touching the string thus at the mid-point of its effective length will raise the produced pitch by one octave; although standard fingering causing an equivalent shortening of the effective length would result in the same rise in pitch, the tone quality produced by harmonic fingering is distinctly different from, and frequently preferred to, that produced by standard fingering. With a normal fretted fingerboard, the commonly-used harmonic points are located directly above frets.
The differences between standard fingering and harmonic fingering can be summarized as follows; standard fingering requires the string to be pressed tightly against the fingerboard between frets, so that the string firmly contacts the adjacent fret; in contrast, harmonic fingering requires minimal touching of the string, typically directly over a fret, and precludes string contact with either a fret or the fingerboard.
2. Description of the Prior Art
The prior art is replete with examples of capos, devices which shorten the effective string length by the mechanical equivalent of standard fingering. A typical capo consists of a laterally-oriented bar spanning all the strings, and fastening means, frequently a strap, which pass under the neck and attach to the ends of the bar, for holding the bar down so that it holds the strings tightly against the fingerboard. Most capos are removable and can be positioned anywhere along the neck of the instrument. The principal use of a capo is to raise the pitch of all the strings by the same amount, so that a player can play the instrument in different keys using the same finger positions relative to the capo as are used relative to the nut when the capo is not in place. Instead of a single bar, some capos include a plurality of adjacent elements mounted in a string-spanning support member, with each element adapted to hold down an individual string. It should be noted that because of the way a capo functions, when a string is held down by a capo, the portion of that string between the capo and the nut is musically useless--i.e, plucking or fingering that portion produces only odd sounds which have no resonance or tone quality. Some examples of prior art capos are shown in the following listed patents:
U.S. Pat. No. 514,263--bar operates on all strings
U.S. Pat. No. 4,503,747--bar operates on all strings
U.S. Pat. No. 4,621,558--bar operates on all strings
U.S. Pat. No. 4,183,279--separate element for each string
U.S. Pat. No. 4,334,457--separate element for each string
British Patent No. 1,048,545 separate element for each string
Regardless of how they are constructed, however, all capos are designed and intended for mounting on the fingerboard between frets and for holding one or more strings against the fingerboard as in standard fingering.